Metal-drawing die.



'C. T. FULLER.

METAL DRAWING DIE,

APPLICATION man NOV-4,1916

Patented Mar. 18,1919.

Inventor: Carl T. Ful ler,

. His Attorneg.

' ley, county of CARL T. FULLER,

oEnU'rLEY, NEW JERSEY, nssrcnon. 'ro GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK.

METAL-DRAWING DIE.

Specification of Letters Patent.

Patented Mar. 18, 1919.

Application filed November 4, 1916. Serial Ito. 129;;78.

To all whom it may concern:

Be it known that I, CARL T. FULLER, a citizen of the United States,

Essex, State of New Jersey, have invented certain'new and useful Imrovements in Metal Drawing Dies, of which the following is a specification.

In drawing tungsten which has been ren I dered ductile by suitable manipulation and mechanical working in a manner now well known in the art, drawing dies of selected diamonds have hitherto been used, as a diamond of good quality was the only material lmown which was hard enough to resist for anylength of time the abrading action of the hard tungsten and was also strong enough to withstand the stresses which tend to split the die. These dies are very expensive, particularly for large wire, and wear away quite rapidly, so that after a moderate length of wire has been drawn, the opening through the die is too large. Many dies are also lost by splitting or during the drawing, operation.

The object of my invention is to reduce the expense of dies in drawing similar hard refractory metal. Another object is to provide a cheap and easily manufactured drawing die which will be suitable for drawing tungsten wire, particularly those sizes which are drawn hot.

I tested metal drawing dies madeof the best grades of tungsten tool steel and also of pure tungsten sintered and consolidated as much as possi lo and found that none of these dies would last long enough to make it worth while to use them. All of them were enlarged so rapidly by the abrasion and wearing away of the walls of the opening that each length of wire drawn was appre ciably larger than the preceding length, and in some cases the diameter of a comparatively short'length of wire was appreciably greater at the end than at the beginning. My tests demonstrated the t-neither the best tungsten steel available nor pure tungsten was of any value for making drawing dies for tungsten'wire. v

In accordance with my invention I consolidate finely divided tungsten by;means. of

residing at Nutbreaking tungsten and 1 slightly larger 5% to 15% of iron into a dense homogeneous drawing die, which has such tensile strength that it does not split or break when tungsten is drawn through it, and which has the remarkable and unexpected property of resisting abrasion so well thatthe opening through it remains of substantially the same size during the drawing of great lengths of tungsten wire, although both the wire and the die are atred heat. A drawing die constructed in accordance with my invention can be made for a small fraction of the cost of a diamond die of the same size and its life is usually a large fraction of that ofthe diamond die, so that a large saving in the cost of drawing tungsten wire is effected by using these drawing dies, particularly for hot drawing the wire to reduce it from the size at which it leaves the swaging machines to the smaller sizes of Wire which may be drawn belowred heat in diaa ond dies without excessive expense for Merely for purposes of illustration I have shown in the accompanying drawing one form in which my invention may be embodied and in which Figure l'is a plan view of one form of die, and Fig. 2 is a longitudinal section through the die and its holder. This particular drawing die 1 is in the form of a,thick disk or short cylinder having a central opening 2. I prefer to mount this die loosely in a suitable holder such as a strong steel block 3 having a pocket 4 deep enough to hold the die securely and than the greatest diameter of the die. The bottom a central opening 5 considerably larger than the opening 2 of the die. I prefer to so shape the die and the holder that the die is supported near its center. For example, if the die is flat, the bottom of the pocket 4: may be slightly conye'x, as shown at 6, or if the pocket has afiat bottom the surface of the die may be slightly convex. In either case the pull of the wire passing through the die in the direction of the arrow seats the central portion of the die firmly on the bottom of the pocket. The die may be held in the pocket 4 by a retaining ring 7.

of the pocket has In operation the holder and die are heated to about 600 0., and the tungsten wire is also heated so that it is red hot when entering the die and is still red hot when emerging from it. Lower temperatures may be used as the wire becomes smaller, but the best results are obtained with these dies when the wire is drawnhot. I

To make the drawing die, I mix finely divided tungsten with finely divided iron to produce a homogeneous powder containing from 5% to 15% of iron, and press this powder in a strong steel mold by a hydraulic press into a disk of the approximate size of the finished die. 'The pressed disk of powder is sufliciently coherent to retain its shape if it is handled with care. The disk of pressed powder is then placed in a boat or on a strip of suitable material, such as 1110- lybdenum, and introduced into an electric furnace comprising a refractory tube of porcelain or alundum with a heating coil wound onit. The disk is heated or fired in the furnace at as high a temperature as possible, usually about 1800 C. in an atmosphere of hydrogen. for about one-half hour. At this temperature and under these conditions the pressed disk does not melt down or lose its shape, but the particles of tungsten are completely consolidated by the iron into a dense coherent block of metal, too hard to be machined, and having even at red heat such tensile strength and remarkable resistance to abrasion that the die made from it can safely be set loosely in the holder 3, as shown in Flg. 2, and used at red heat without danger of splitting.

To facilitate making the die a-perforation smaller than the openmg in the finished die may be made through the disk of pressed powder and then be enlarged to the proper size after the disk has been fired.

I have found that the best results are obtained with a mixture composed of about 90% by weight of powdered tungsten and- 10% by weight of powdered iron, although good results are obtained where the iron is I as little as 5% or as great as 15%. If these limits are exceeded the die does not have the "its homogeneous at the temperature attained 'in the electrle furnaceand also at all lower long life and resistant-,8 to abrasion characteristlc of the die having the proper amount of iron.

While I do notwish to advance any theor as to the nature of the metal forming the (he, it is highly probable that the iron and thetungsten form a solid solution which temperatures, particularly at about red heat; 'I have securedthe; best results by making the dies from unwrought tungsten metal obtained in the form .of powder by reducing tungstic oxid, arranged in a layer not more than an inch deep, in a refractory tube through which a current of pure, dry hydrogen is passedwhile the temperature of the tube is slowly raised so that in six or seven hours it attains a temperature of 900 or 1100 C. The object of this procedure is to secure the tungsten metal in the form of a grayish powder, such as is used in manu faeturing drawn wire filaments, and coarser than the very black impalpable tungsten powder such as was generally used in manufacturing lamp filaments by the squirting process. This tungsten metal may to advantage be the same as is commonly used to make ductile tungsten. This metal contains about 1% or less of thorium oXid.

The iron and the trungsten may be inticedure which I prefer and by which I have obtained the best results, is as follows: 500 grams of ferrous sulfate is dissolved in about four liters of water and ammonia water is added gradually to the solution while the whole mass is agitated by means of an air jet until the ferrous hydrate is precipitated. About 1 liter more of water is added and the precipitate allowed to settle, after which the precipitate is washed, preferably by agitating it with water, ermitting it to settle, and siphoning ofi or ecanting the supernatant liquid. The ferrous hydrate is washed until free from ammonium salts. The moist fer rous hydrate is then poured into a porcelain evaporating dish containing 900 grams of the powdered tungsten metal prepared as above described. The contents of the dish are well mixed and then dried, preferably on a hot plate or by steam. The resultant dried mass is then placed .inshallow sheet iron boats in charges of about 300 grams each, and reduced in hydrogen gas in an electric furnace comprising a refractory tube through which the hydrogen flows. This tube is kept, at its hottest part, at a temperature from 23 to 25% of the temperature of the filament of a carbon lamp operating at an efliciency of 3.1 watts per candle. The hydrogen should be well dried by sulfuric acid and phosphorus pentoxid. I The furnace should be so arranged that the sheet iron boats pass. through the hot zone ofthe furnace at the rate of about one-half inch per minute and on into a cool end portion, which ma be of iron and water cooled.

- fter the boats are removed from the cool powder. containing approximately 10% iron and 90% tungsten and very suitable for the manufacture of metal drawing dies by press ing and firing in the manner above described.

What I claim as new and desire to secure by Letters Patent of the United States, is,-' 1. A metal die for wire drawing at about red heat consisting of an alloy of iron and timgsten containing between 5% and 15% of Iron. c

2. A metal die for wire drawing consisting of an alloy of iron and tungsten contaming substantially ten per cent. of iron.

In witness whereof, I hereunto set my hand this second day of November, 1916.

CARL T. FULLER. 

